Trouble in a new DIY amp.

andRookie · 26th March 2007, 09:19 AM

I've built a PP EL34 following the Lundal/Byrith document, but used hashimoto 40-5 transformer and bulit the of PSUs different.

I can turn it on with dummy load attached and measure the DC - levels thrugh both channels. They are fine, and so are the heather voltages. Tubes also seemes fine. Bias is -28 at grid, 460mV over the catode res. Some hum in one channel, the other is very silent.

Connected a CD-player and a pre to it yesterday. One channel played fine a while, the other was still silent. Only a faint hum was audible. Tried switching input connections, but when I turned it on again the secondary fuse (500mA, just before B+ tap in the HT-psu) was blown.

I have some pdf and powerpoint schematics I`ve drawn, but I do not know how to upload them. I do also get a lot of help on a norwegian forum. I`ll post if we find some faults.

singa · 26th March 2007, 09:40 AM

Hi,
Just guessing, since one channel does not work,there may be a connection/wiring problem.The fuse may be rated too low if the transformer is a large one.TRy 1A onwards.
Cheers.

andRookie · 26th March 2007, 10:15 AM

There is a 2A fuse on the primary of the xformer. The fuse in the B+ was supposed to be 300mA, but only I had a 500mA availible.

singa · 26th March 2007, 10:22 AM

Hi,
Better recheck wiring of defective channel .Good luck.

alexmoose · 26th March 2007, 05:08 PM

A paticularly trickey place to check is the coupling between the driver stage and the output stage, make sure you are getting good levels of resistance, Make sure the cap isn't leaking DC, and make sure the coupling stage isn't shorting anything to ground.

andRookie · 27th March 2007, 12:14 PM

Found a wire break to the grid of one EF86, so that explained the lack of signal. For the fuse, C filter takes a while to reach max, so when the cathodes are hot (fuse popped when I turned on - of - and on again) the fuse pops. I'll rebulid a delay circuit so it does not encompass the C filter, only B filter.

alexmoose · 28th March 2007, 04:36 PM

any new updates? I am now intrigued

andRookie · 28th March 2007, 06:12 PM

Still working on it.

Dave Cigna · 28th March 2007, 11:14 PM

What are you using for power transformers? Are the toroids by any chance? Toroids, by nature of the remanence of the core, will sometimes blow a fuse when powered up. It has to do with the phase of the AC when turned off, then the phase when turned on again. I once had it figured out what set of conditions result in trouble, but my memory... It doesn't matter...

I have also had the problem with seriously oversized EI transformers, though I have not figured out why.

-- Dave

andRookie · 29th March 2007, 08:47 AM

Its not a toroid, but a dynaco - replacement thing from triodeelectronics. Seems to be running quite cool and with low hum, buy the way.

26th March 2007, 09:19 AM	#1
andRookie diyAudio Member Join Date: Apr 2006 Location: up north	Trouble in a new DIY amp. I've built a PP EL34 following the Lundal/Byrith document, but used hashimoto 40-5 transformer and bulit the of PSUs different. I can turn it on with dummy load attached and measure the DC - levels thrugh both channels. They are fine, and so are the heather voltages. Tubes also seemes fine. Bias is -28 at grid, 460mV over the catode res. Some hum in one channel, the other is very silent. Connected a CD-player and a pre to it yesterday. One channel played fine a while, the other was still silent. Only a faint hum was audible. Tried switching input connections, but when I turned it on again the secondary fuse (500mA, just before B+ tap in the HT-psu) was blown. I have some pdf and powerpoint schematics I`ve drawn, but I do not know how to upload them. I do also get a lot of help on a norwegian forum. I`ll post if we find some faults.

28th March 2007, 11:14 PM	#9
Dave Cigna diyAudio Member Join Date: Oct 2003 Location: Finger Lakes, NY	What are you using for power transformers? Are the toroids by any chance? Toroids, by nature of the remanence of the core, will sometimes blow a fuse when powered up. It has to do with the phase of the AC when turned off, then the phase when turned on again. I once had it figured out what set of conditions result in trouble, but my memory... It doesn't matter... I have also had the problem with seriously oversized EI transformers, though I have not figured out why. -- Dave __________________ January 20, 2009: Bush's last day

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26th March 2007, 09:40 AM	#2
singa diyAudio Member Join Date: Apr 2004 Location: near	Hi, Just guessing, since one channel does not work,there may be a connection/wiring problem.The fuse may be rated too low if the transformer is a large one.TRy 1A onwards. Cheers.

26th March 2007, 10:15 AM	#3
andRookie diyAudio Member Join Date: Apr 2006 Location: up north	There is a 2A fuse on the primary of the xformer. The fuse in the B+ was supposed to be 300mA, but only I had a 500mA availible.

26th March 2007, 10:22 AM	#4
singa diyAudio Member Join Date: Apr 2004 Location: near	Hi, Better recheck wiring of defective channel .Good luck.

26th March 2007, 05:08 PM	#5
alexmoose diyAudio Member Join Date: Mar 2006 Location: Michigan	A paticularly trickey place to check is the coupling between the driver stage and the output stage, make sure you are getting good levels of resistance, Make sure the cap isn't leaking DC, and make sure the coupling stage isn't shorting anything to ground.

27th March 2007, 12:14 PM	#6
andRookie diyAudio Member Join Date: Apr 2006 Location: up north	Found a wire break to the grid of one EF86, so that explained the lack of signal. For the fuse, C filter takes a while to reach max, so when the cathodes are hot (fuse popped when I turned on - of - and on again) the fuse pops. I'll rebulid a delay circuit so it does not encompass the C filter, only B filter.

28th March 2007, 04:36 PM	#7
alexmoose diyAudio Member Join Date: Mar 2006 Location: Michigan	any new updates? I am now intrigued

28th March 2007, 06:12 PM	#8
andRookie diyAudio Member Join Date: Apr 2006 Location: up north	Still working on it.

29th March 2007, 08:47 AM	#10
andRookie diyAudio Member Join Date: Apr 2006 Location: up north	Its not a toroid, but a dynaco - replacement thing from triodeelectronics. Seems to be running quite cool and with low hum, buy the way.

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